I was just doing a small sanding job on the bottom front of my 6’6 with 320 grit wet & dry when I noticed the following: my hand slides more quickly over the sanded surface, then seems to slow when it hits the polished back half. I know that conventional wisdom stated here and elsewhere says the more polished the surface, the faster (America’s Cup and 1000 grit etc) but I wonder of the validity of that, especially when so many rough “sanded finish” boards seem to be the magic ones. I also realize that my hand pressure is not water, I just wonder if there can be something faster about a slightly textured surface (ie slightly rougher. The Speedskins used by Olympic swimmers are actually textured and work on the theory of capturing water molecules against the pseudo-skin to lubricate other water molecules). I wonder if a slightly rough surfboard finish might be likewise slicker and faster than a polished one. (?)
I know for a fact that a snowboard will stick to wet spring snow if the surface is slick. It creates a suction effect. Grooves along the running length of the board helps enormously. I’m wondering if the same effect is happening on the surfboards. It will be hard to prove though, because it’s so hard to create a controlable test enviroment. I’d like to try this though: 1) Gather equipment: One large smooth table. One piece of plywood. Some glass and resin. Water 2) glass the plywood on one side, sand, gloss, polish, etc. 3) Water the table. Run the plywood over the table in the water. Messure friction forces. 4) Sand the glassed plywood with whatever grit you prefere in whatever direction you prefere. 5) Repeat 3. 6) Repeat 4 with different grit and/or direction, then go to 5 again, keep going until bored or finding a results. I’m not sure this is really what’s going on or if it even applies to a surface running over deeper/thicker ‘layer’ of water. There is certainly other effect in play too. But it’s my theory and I’m sticking with it(atleast for now). regards, Håvard
Water “sticks” to surfaces due to a combination of surface texture and surface tension. While a dimpled (rough) texture on a non-streamlined body can lengthen laminar flow by energizing the flow a streamlined object like a surfboard won’t benefit from the “golf ball effect.” (I do recommend using a hammer to put dimples on SurfTechs). While the hand does indeed flow much easier over a sanded board skin, oils and body heat are much different than sea water. But the simple hand experiment may illustrate the effects of surface tension rather than texture. Surface tension effects the interaction of water and board. The surface tension of a sanded board is probably faster than a glossed board. Sanding probably changes the surface of the board at the molecular level which will change the surface tension. Surfactants greatly reduce the surface tension of water. A surfactant is a chemical whose molecules have a hydrophobic segment and a hydrophilic segment. This partial solubility allows this molecule to occupy the space at the water/board interface. One big problem with sanded boards is they get dirty quick. If you like a glossed board and want to experiment with surfactants I would recommend McLube. It is designed and used in the sailboat world for a variety of purposes. It created a protective surface which can keep a sanded bottom cleaner and make removing wax from board bags very simple. I’ve used it on glossed boards. It seems to last more than a month per spray and is not expensive. Spray the board in a vertical position so large aerosol drops do not stick to the bottom. Rob Olliges
What about Windex-designed to keep the windscreen (what do Americans call the windscreen?) clear whilst driving in heavy rain…i don’t need to even use wipers when i have windex on my windscreen.
No need for low friction surfaces! More horsepower is the answer! http://22.214.171.124/cgi-bin/linkrd?_lang=EN&lah=c11acf3c4b2fe675ee8d570ccaeed8d2&lat=1063213376&hm___action=http%3a%2f%2fwww%2epowerski%2ecom%2fengineering%2ehtml
Laird Hamilton has been testing them and helping with development. What`s the world coming to?
Interestingly yesterday I visited a swimming pool slide manufacturer. They make all their slides textured. Appearently they work much better that way. Is this relative to the conversation here? Is there any reason to buff a surfboard to a high gloss? Why do we waste so much time and energy (money) on something that reduces performance?
Seems a couple different physical phenomonons are being crossed here. Smoother can mean more friction, simple put, there is more contact area. As a surface gets rougher there’s less to contact. Your hand is compliant, and will form to the surface, rigid object can slide with much more ease. Now if the moving object’s size is on the order of the surface roughness, then you will have a different situation. Furthermore, uneven roughness will have physical barriers that would slow a sliding object down. Disc’s (air hockey) or other objects that can trap a layer of air are a whole other matter. Liquid/solid interfaces are different. Although it’s not totally true, you can assume a ‘no slip surface’ on the bottom of your surfboard - the water in contact remains in contact. This creates a thin area of high shear called a boundary layer. Outside of this boundary layer is where the water is really moving, hopefully in a laminar fashion.
Rook, a rougher surface has more surface area. More nooks and crannies. Like a ragged coastline. Greg, a pool slide needs to be kept wet so kids don’t stick (burn butt & leg skin) on the way down. The texture on slides is probably to distribute the water over the entire slide and to trap a little bit in place. On those smooth slides the water tends to leave a lot of dry spots. BTW, isn’t Additive F a surfactant? Does it help to let epoxy resin flow and also change the molecular surface that is exposed to air? Rob Olliges http://www.888teammclube.com/frames/sailkote/index.html
OK, lots of thoughts provoked-all good. Now, anybody hear of those competitive textured swim body suits? They were rumored to be responsible for taking several seconds off of top swimmer’s times. Again, a textured surface designed to hold a thin layer of water to lubricate and lower friction. Would it work on a board too?
The running surface (rails/bottom) on my surf mats holds a thin layer of water… a slippery, almost slime-like feeling. Very fast and free.
Interesting indeed about the water slides. It sounds like the pressure of a slider could push water out from underneath and lead to more friction and loss of speed. Maybe not directly the same as surfing since water will always (hopefully) be under one’s board. But it does show the importance a less-than-perfectly flat surface can offer with regards to lubrication. I remember from about twenty years ago when some guys experimented making ridges in the bottom of their boards in their gloss coats to try to mimick the efficient laminar flow found on certain whales. Sounded very fiddlesome and difficult. But maybe making shallow grooves perhaps 80 grit down the length of boards bottoms? Easy to do. Or “shark scales” like the topography of the Speedskins- more difficult. I like the idea of the Pedersen Fireball Fish’s twisted channel wild water flow concept, but maybe that is overrcooking an idea that could be beneficial at a much more subtle level.
Rook, a rougher surface has more surface area. More nooks and crannies. Like a ragged coastline Yes, too your hand, which conforms, or to a fluid. But not to a rigid solid. It only contacts with the tips of the bumps…
Rook, a rougher surface has more surface area. More nooks and crannies. Like a ragged coastline>>>>Yes, too your hand, which conforms, or to a fluid. But not to a rigid solid. It only contacts with the tips of the bumps… Like a bed of nails? : ) Rob Olliges
So maybe it’s time to get Dale in on this. His mats don’t have a slick finish and yet they appear to be the fastest surfing vehicle. Any comments?
Greg, My surf mats’ running surface is a non-permeable and supple, mil-spec 70 denier nylon taffeta. If you pass your hand along the bottom when it
s wet and properly inflated (very low pressure), the surface instantly rises and falls... conforming to the shape of the source of pressure. The bottom and edges of the mat literally try to "flow" around whatever is pressing against it... in actual use, its the curve and texture of the wave, combined with the force and angle of the rider. A mat
s primary function is multi-directional adaptability, i.e. seeking the paths of least resistance. In addition to the wave, the riders body position and freehand squeezing of the front corners and edges both increase and/or decrease the internal pressure, which directly affects the rocker/torque, rail contours, thickness flow/buoyancy distribution and template/corner shape. Obviously, at only 18-20 ounces, they
re extremely sensitive. Seemingly insignificant details (such as running surface texture) do add up, and contribute to overall performance. If a designs elements are operating in balance, the whole should be greater than the sum of its parts. So, in answer to your question, the texture of the mat
s "footprint" while moving across a wave, is only one part of why theyre so efficient.
greg liddle advocated a lightgrit sanding lengthwise on an unglossed bottom (pertaining to hulls) to enhance speed.